Test the earth without breaking it
Clamp-on earth testers for looped grounding systems. Three models across two jaw sizes, reading loop resistance from 0.01 Ω with no auxiliary rods and no disconnection, and true RMS leakage current to 20 A on the C models. Filter by jaw shape, range and whether you need current measurement.
Filter by what matters to you
Select any combination of criteria. Choosing more than one option within a row widens the search rather than narrowing it.
| Model | Jaw | Jaw opening | Resistance range | Best accuracy | Leakage current | Data upload | Link to product page |
|---|---|---|---|---|---|---|---|
| ERT-15C | Round jaw | Round Ø32 mm | 0.01 to 200 Ω | ±(1% + 0.01 Ω) | — | — | View product |
| ERT-20C | Long jaw | 65 × 32 mm | 0.01 to 1200 Ω | ±(1% + 0.01 Ω) | 0.0 mA to 20.0 A | — | View product |
| ERT-20C+ | Long jaw | 65 × 32 mm | 0.01 to 1200 Ω | ±(1% + 0.01 Ω) | 0.0 mA to 20.0 A | RS232 + software | View product |
Two jaw sizes
Same measurement principle, same keypad and memory. The opening decides what you can get the instrument around, and the long jaw adds range and current measurement.
ERT-15C
Round Jaw Clamp Earth Tester
A circular Ø32 mm opening that takes a round conductor up to 32 mm across. Reads earth loop resistance from 0.01 Ω to 200 Ω, and it is the shortest and lightest of the range.
ERT-20C / 20C+
Long Jaw Clamp Earth Tester
A 65 × 32 mm elliptic opening that swallows flat earthing tape. Extends to 1200 Ω and adds true RMS leakage current to 20 A, with RS232 upload on the plus model.
Four things worth settling first
Is the earth already in a loop?
A clamp tester measures the resistance of a closed loop. On a tower line, a cable-shield network or a bonded building grid that is exactly what you want. A single isolated electrode has no loop and cannot be read directly, so bond it to a second known-good electrode, or use one of the stake-type testers in our earth testing kits.
Match the jaw to the conductor, not the number
The round jaw takes a wider round conductor at 32 mm; the long jaw spans 65 mm across flat tape but only 28 mm through the round axis. If you are clamping cable rather than tape, the ERT-15C may be the one that fits.
Look at where the accuracy sits
Both models are ±(1% + 0.01 Ω) below 1 Ω, which is where earthing work is normally judged. Accuracy widens with range, reaching ±(25% + 30 Ω) at the top of the 1200 Ω span, so treat high readings as indicative.
Do you need to see the current?
Leakage and neutral current to 20 A true RMS is on the C models only. It is what tells you whether a high resistance reading is a real fault or interference circulating in the loop, and it is worth having on a survey instrument.